In order to reduce tracking errors and pilot workload, a pilot may be provided with increased situational awareness of an aircraft with respect to a desired flight path. In particular, a pilot must be aware of the actual aircraft performance, or flight path vector (FPV), the desired or commanded aircraft performance, and the predicted aircraft performance. The use of a perspective display with a predictive flight path or performance symbology set provides increased situational awareness. Perspective displays with predictive symbology permit a pilot to “see” what will be required or demanded of the aircraft to maintain a desired flight path, as well as where the aircraft will be in a finite period of time. With the increased situational awareness, the pilot's workload is lower, thereby permitting better flight management.
Flight director guidance for critical maneuvers, such as those maneuvers with very small or reduced margins for error, is often essential for precision navigation requirements. Current flight guidance display sets utilize symbology that is based on compensatory tracking tasks or follow a guidance cue to satisfy (i.e., null) an error signal. Further, current generations of terrain flight guidance systems use radiated emissions and track errors displayed using compensatory tracking symbology (e.g., Delta-Veebar and Two-bar). Such systems operate satisfactorily, but are limited in their ability to display future flight path information to the pilot and/or the results of pilot control input. The display symbology sets are designed to follow command guidance from an off-course situation to return to a nominal (i.e., null error) solution, known as a compensatory tracking task. Thus, such displays cause much “mental gymnastics”, cognitive processing, and pilot mental workload, which may lead to additional error.
This traditional symbology used for instrument approaches in vertical flight aircraft, such as rotorcraft or tiltrotors, is based on compensatory tracking tasks. Compensatory tracking tasks are derived by monitoring actual aircraft performance against commanded performance during flight and actual cross-track error against commanded cross-track during flight. Guidance errors are generally computed as the difference between guidance commands and sensed aircraft state. The errors are sent to flight director controls, which generate steering commands. These commands appear as flight director symbology on a cockpit display and direct the pilot where to position the lateral stick (roll), thrust control lever (power), and the longitudinal stick (pitch). If the pilot responds with the appropriate control inputs to satisfy the flight director steering commands, the aircraft will converge on the reference values selected.
Symbology based on compensatory tracking tasks is designed to provide the pilot with command guidance instructing a pilot to make flight adjustments to guide an aircraft from an off-course situation to return to a nominal or null error solution. However, compensatory tracking symbology does not provide the pilot with information indicating how far the aircraft is off course or what flight control input is required to regain course centerline. Therefore, the pilot must constantly monitor flight commands and the results of control inputs.
Furthermore, compensatory tracking does not provide flight path predictability, and displays that utilize compensatory symbology typically require more cognitive processing by the pilot. This causes heavy pilot mental workload that may lead to errors, especially in high workload constrained terminal areas or during low altitude operations. For example, excessive pilot mental workload can lead to full-scale deflection errors or total loss of situational awareness resulting in a maximum deviation mandated missed approach. Thus, compensatory symbology often creates display clutter and high pilot cognitive workload, which increases the risk of flight technical errors (FTE's).
To overcome the shortcomings of guidance systems and symbology based on compensatory tracking tasks, perspective display sets, or three-dimensional (3D) displays, have been developed. Most perspective display sets provide 3D tunnels consisting of a series of rectangles connected by lines through the corners. In particular, perspective display sets are useful for terrain following/terrain avoidance (TF/TA) flights that require accurate elevation and obstacle data for use by aircraft flight director systems to provide the pilot with immediate, real-time flight guidance information. The traditional systems for providing this information and the symbology used for TF/TA aircraft attitude based operations and “null command” compensatory tracking systems are based on radiated/returned sensor data.
Current methodology for guidance for TF/TA operations utilize energy-emitting radiation systems or a multi-mode radar to provide a real-time display of terrain/obstacles ahead of the aircraft. These systems, while accurate, are limited in that the display and data are restricted by the performance of the sensor system. For example, turning limitations from the turn rate/bank angle limiter on some multi-mode radars precludes the system from “seeing” around or into the turn. Further, and for example, current sensor-based systems cannot provide the pilot with reliable “nose over” cueing to enable terrain flight because the emitter sensor cannot “look over” the terrain ahead, but must rely on line-of-sight (LOS) operation.
It is desirable to develop a system and perspective display set that yields better performance results than current navigation systems and perspective symbology sets, as well as providing look ahead functionality and increased situational awareness, causing less display clutter, reducing pilot work load and reducing FTE's.